CH Bathymetric Data Acquisition & Processing 2

Question 1

Which sonar beam geometry best describes a multibeam echosounder (MBES) system?

Accepted Answer

A fan of beams projected perpendicular to the vessel track

Answer

MBES systems transmit a fan of beams oriented across track, enabling wide swath coverage in a single pass.

Question 2

When processing MBES data, what is the primary purpose of applying a sound velocity profile (SVP)?

Accepted Answer

To compensate for beam refraction caused by water column velocity gradients

Answer

SVP corrections account for ray bending (refraction) as acoustic beams travel through water layers with different sound velocities.

Question 3

A hydrographer notices outer-beam soundings consistently read shallower than inner-beam soundings over flat bottom. The most likely cause is:

Accepted Answer

An incorrectly entered sound velocity at the sonar head

Answer

Using an incorrect surface sound velocity at the transducer face causes outer beams to refract incorrectly, producing characteristic 'smiling' or 'frowning' artifacts.

Question 4

In IHO S-44 standards, the 'Special Order' survey category is primarily intended for:

Accepted Answer

Areas where under-keel clearance is critical, such as harbor entrances

Answer

Special Order is the most stringent IHO category, reserved for critical harbor, berthing, and canal areas where every seafloor feature must be detected.

Question 5

What does the term 'patch test' refer to in multibeam survey operations?

Accepted Answer

A field calibration procedure to determine transducer mounting angle offsets

Answer

A patch test (or MBES calibration run) measures residual pitch, roll, yaw, and latency offsets in the transducer installation.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Bathymetric Data Acquisition & Processing 2